This invention relates to organic conductors and semiconductors which are thermoformable conductive polyblends. More particularly, this invention relates to a conductive polyblend in which a pyrrole monomer is polymerized in situ, in a solution of a matrix polymer, by contacting the monomer with a polymerization initiator. The polyblend so formed is imbued with the desirable characteristics of the matrix polymer, yet acquires the conductivity derived from the presence of conductive polypyrrole. The term "polypyrrole" is used herein to connote a polymer of pyrrole or pyrrole substituted at one or both of its 3- and 4- positions.
As is well known, conducting polypyrroles defy conventional melt-processing, cannot be compacted, whether molded or extruded, in the usual ways, nor deposited as a continuous film from solution; and, they are far from stable in air even at ambient temperature conditions. A polymer which defies compaction into a shaped article, places severe limitations upon its use. Certain pyrrole polymers made by electrodeposition are found to be compactable (see copending U.S. patent application Ser. No. 486,161, filed Apr. 18, 1983), now U.S. Pat. No. 4,543,402, and to form self-supporting films, but this process is too slow for general commercial utility.
In copending application Ser. No. 618,701 filed June 8, 1984, now abandoned, I have disclosed a chemical process for coating an electrically non-conductive substrate such as poly(vinyl chloride) and certain inorganic materials, with a coating of conductive polypyrrole. Though this process is fast, only the coating of polypyrrole is conductive while the substrate under the coating remains non-conducting.
In many instances, particularly for fiber-reinforced synthetic resinous materials, and for high strength polyblends such as those commercially available as Noryl.RTM. blend of styrene and poly(phenylene oxide), it was desirable to make the body of the resin conductive, not just the surface. Such instances arise when it is likely that a conductor will suffer surface damage but it is essential that such damage not affect the conductivity of the conductor. In other instances it is insufficient to provide only surface conductivity, as for example, in the preparation of porous conductive polymer membranes. Apart from those instances, such as those recited, where conductivity of the polymer mass is essential, it will be evident that being forced to provide an article of arbitrary shape with a conductive surface severely limits the options available as compared with those available when the entire body is conductive.
The problem was to find a relatively fast non-electrochemical process which yielded a thermoformable polyblend conductor (the term "conductor" as used herein includes semiconductors) so that the polypyrroles formed as part of the polyblend might be more versatile in their applications.
By "semiconductors" I refer to polymers of pyrrole/substituted pyrrole monomers which have relatively low conductivity in the range from about 10.sup.-3 ohm.sup.-1 cm.sup.-1 ("S/cm" for convenience to indicate reciprocal ohms/cm) to 1 S/cm, while "conductors" have a conductivity in the relatively high range of from 1 to about 150 S/cm.
Poly(2,5-pyrrole) (referred to herein as "PP" for brevity), in which the --NH-- group links sequences of conjugated double bonds, is normally an insulator, that is, has a conductivity less than about 10.sup.-10 S/cm and is totally insoluble in known solvents. It is known however, that electrochemically polymerized PP has good conductivity, but coupled with its melt-processing-resistance and the poor integrity of PP film so formed, it was deemed more desirable to produce the PP with a chemical process. Others have also sought to do so. In particular, German (FDR) Offenlegungsshrift DE No. 3321281 A1 published Dec. 22, 1983 discloses a chemical process for producing a conductive paper by impregnating the paper with different concentrations of an aqueous ferric chloride solution which is acidified with HCl, then exposing the impregnated paper to pyrrole monomer, usually in the gaseous phase. Further details of this process are disclosed in an article titled "Some Properties of Polypyrrole-Paper Composities" by Bjorklund, R. B. and Lundstroem, I., Journal of Electronic Materials, Vol. 13, No. 1, 1984.
As also stated in Bjorklund et al, they were aware that anhydrous FeCl.sub.3 used as a dopant with poly-p-phenylene exists as an FeCl.sub.4 (2.sup.-) complex in the polymer matrix, thus imparting conductivity to the polymer. Other polymers, for example polyacetylene impregnated with FeCl.sub.3 or other oxidants such as SbCl.sub.5, and, neutral polypyrrole which is exposed to FeCl.sub.3 vapor or an anhydrous solution of the electrolyte, is also made conductive. But impregnating a preformed polymer with FeCl.sub.3 to make it conductive does not suggest that one may use anhydrous FeCl.sub.3 as an initiator to form the polymer from the pyrrole monomer, or that the FeCl.sub.3 would generate a charged species in the polymer formed. As is well-known, poly-p-phenylene cannot be formed by initiation with FeCl.sub.3 (see "Reaction of Ferric Chloride with Benzene", by P. Kovacic and C. Wu, J. Polym. Sci. Vol XLVII pg. 45-54 at pg. 45, first sentence of "Results", 1960), and the polymer is not conductive unless post-treated with FeCl.sub.3.
With respect to polymers of 3- and/or 4- substituted pyrroles ("subs PP"), Bjorklund et al corroborate the generally well known fact that providing substituents on pyrrole does not improve the conductivity of the subs PP. Yet, with the process of my invention, a polyblend containing a minor amount by weight of a designated subs PP has relatively good conductivity.
As noted by Bjorklund et al, their precipitated PP was compactable under 10 ton pressure to form a wafer. Polyblends formed with PP/subs PP precipitated in situ by my polymerization reaction is compacted and thermoformed by extrusion, injection molding and the like, under substantially the same conditions as those for the matrix polymer which forms the major component by wt. in the polyblend.